I have a 1998 Volvo S70 GLT with 185K miles on it. When the weather is cold the car has a rough idle and vibration that emanates from the right side of the engine. It feels like the car is not running on all five cylinders. It does not have full power, but does not stall. I've gotten the car tuned up and had the various belt pulleys replaced as needed over the years to stop squeaks and vibrations, but this one has a top independent Volvo shop mechanic baffled. The vibration goes away completely when the car has been running for about 20 minutes. It's worse at temps below 30 degrees F. Also, I have a low frequency whine coming from the engine for the first five minutes of operation that is definitely not the smog pump because I can hear that winding down. I'm surprised that I have not seen anyone else with this problem on any forums. Thanks for any ideas. I recently stalled on a sub freezing night and got the car going after putting some dry gas in the tank. A bottle of Sea Foam recently improved overall performance at high revs but did not help the cold vibration. The shop could not duplicate the stalling. The air meter was replaced this past summer. There is a weld repair on the front of the the exhaust system that makes a bit of noise until the car warms up.

The '98 model year was a split year for the timing belt tensioner. Cars build earlier for that model year have an "automatic" or hydraulic tensioner. Cars build later for that model year have what's called a "manual" tensioner which happens to be temperature sensitive. In other words, when it is installed, depending on the temperature at the time, it is adjusted accordingly. I'm wondering if this might not be your problem. Could be that it is just a bit off, but by the time the engine really warms up the problems go away. This would explain the vibrations on the right side (if I'm reading you right, this would be the TB side, right?)- most likely scenario is that your timing is slighly off at lower temperatures. Guess my questions are, do you know if your car has the earlier hydraulic tensioner or the later manual tensioner, and how long has this been going on- since the TB was last changed? Or, is it possilbe that the belt never been changed? I know it's a bit early, at 185K miles to change the belt and tensioner again (if it's been changed before- suppose to be every 70K miles on your car), but it might be worth it to at least have this checked. As all of our FWD/AWD Volvo's have interference engines, if the tensioner causes the TB to break, that's the end of our engines, so don't delay in this.

I may be totally off in my theory above, but I may not.Let us know what you know about the history of your car's Timing Belt and tensioner.

I like the manual timing belt tensioner theory. I have been overly cautious maintaining the car and I have changed the timing belt twice. The last time I had it done was while one of the tensinoners on the alternator belt was being replaced about 15K miles ago this past summer. My goal is to get 300K miles out of this car. The car has always had this cold vibration since I bought it used at 37K miles, but not as bad as recently.

I'll ask my mechanic if he can tell me whether or not this car has a manual tensioner. If it does, what would be the best thing to do? If is adjusted for colder temps. this time of year would that lead to problems when I ran it during the summer heat?? It was installed in the summer.

Also, when the car stalled during the first cold snap of the season I did have the check engine light come on, but the mechanic was not impressed by what the code said. This guy has been fixing Volvos for years and said that the S70 does not usually have problems with water in the fuel, which I thought was in interesting observation. If he thinks that it must be because Volvo owners are careful about using dry gas!?

It's nice to have a good mechanic that you trust...he is correct about rare to have water in the gas (although buying cheap gas can cause some strange issues in our turbos). That said, yes, definitely ask him about the tensioner. Setting it correctly if installed in the summer shouldn't cause issues when it gets colder unless the center screw in it somehow slipped during the months it was driven. You're suppose to counter hold it as you make the adjustment. I don't know specifics on it except for what I've read but plan to do our V70's tensioner when the time comes (still a few years away, hopefully). The only other thing that comes to mind about your car is that possibly the vibration and poor idle in the cold could be due to incorrectly gapped spark plugs or the use of double platinum Bosch plugs (our cars for some reason hate these), so if this is the case, it would be a very easy (and cheap) repair to switch to copper core Bosch's gapped at 0.028 inches.

Once again, good luck and please keep us posted on what is ultimately the solution to your current issues with the S70...Oh, and Happy New Year!